The mammal skin comprises various kinds of cells, performs a variety of functions and includes diverse chemical compositions. A variety of lipids exist between the different skin layers in various concentrations. Specifically, the dermis of skin consists of fibroblasts that mainly produce collagen and other proteins and a small quantity of lipid. On the contrary, the epidermis includes keratinocytes that produce the lipid but does not substantially produce the collagen. The collagen produced by the fibroblasts endows the skin with an extension strength and the lipid produced by the keratinocytes forms an interruption layer between a living tissue and an external to perform a skin barrier function.
As lipid ingredients in the skin, there are phosphatidylserine, phosphatidylethanolamine, phosphatidylinositol, triglyceride, glucosylceramide, ceramide, cholesterol, cholesterol sulfate, free fatty acids and the like. Among them, phosphatidylserine, phosphatidylethanolamine, phosphatidylinositol and the like that are phospholipids are distributed in the dermis and the ceramide-based materials are mainly distributed in the epidermis. The distribution ratio of the compositions and the lipid amount contribute to a skin barrier maintenance homeostasis and provide a rapid restoration action against external physical and chemical injuries.
The epidermis lipid during the aging is generally reduced contrary to the otherwise epidermis tissue, so that the skin barrier function is decreased. In addition, an overall epidermis lipid is reduced to a degree of about 30% of the young people, but each content proportion of the lipids is maintained. This validates that the lipids of the skin keratin are produced through lipid biosynthesis and ceramide biosynthesis pathways. It has been reported that the lipids of the skin keratin are actually derived from the phospholipids and the free fatty acids of the dermis [Hamanaka et al., J. Invsti. Dermatol., 119, pp 416-423, 2002]. It has been also known that the skin proceeds to an aging skin as the ratio of the free fatty acids is changed [Rogers et al., Arch. Dermatol. Res. 288, pp 765-770, 1996].
The phosphatidylserine is a kind of the lipids present in the nature and a material consisting of serine group, phosphate group, glycerol and two fatty acid groups connected each other. A weight of lecithin occupies about a half of a dry weight of a human brain. Most of lecithin forms a nerve cell membrane. The phosphatidylserine is a kind of lecithin derivatives that are important ingredients of the cell membrane and present particularly in plenty in the brain. It seems that the phosphatidylserine is deeply concerned with function expressions of the nerve cells, for example energy flow for a life-support activity in the nerve cell membrane and information transfer such as neurotransmitter discharge or synapse activity. However, although the phosphatidylserine is present in plenty in the brain of an animal, it is present less than a concentration of 0.1% in the origin except the brain of the animal, so that it is difficult to obtain the phosphatidylserine in a large quantity from natural raw materials.
It has been recently known peroxisome proliferators activated receptors (PPAR) existing in skin constituting cells on the whole. It has been clarified that the PPAR plays an important role in expressions of the barrier restoration and inflammation healing processes of the skin.
Specifically, the PPAR is a factor of regulating the energy homeostasis. It has been known that the PPAR is concerned with the skin state regulation such as permeability regulation of the skin barrier, epidermis layer multiplication inhibition, differentiation induction of the epidermis layer and the like through various mechanism. Due to the properties, the PPAR acts as a core regulator of diverse skin diseases such as psoriasis, wound healing and acnes due to hyperplasia of the epidermis layer as well as inflammation related skin diseases.
Accordingly, although it has not been much known a specified signal transfer of a material contributing to the skin homeostasis, it is attempted a specific research on functions of the phospholipids related to the PPAR which has been recently known. It is known that the PPAR has three subtypes. Among them, it has been clarified that PPAR-a has a possibility of a receptor of the phosphatidylserine [Michalik et. al., The Journal of Cell Biology, 154, pp 799-814, 2001].
In actual fact, it has been clarified that when clofibrate, WY14643 and the like, which are already known-agonists of the PPAR-a, are applied to the skin, the inflammation due to the skin stimulating material is decreased [Sheu et. al., The Journal of Investigative Dermatology, 118, pp 94-101, 2002].
Up to date, materials such as glucocorticoid have been used as anti-inflammatory agent. However, if continuous administration or treatment thereof is conducted, a chronic side-effect is caused, so that an immunological reaction is mainly decreased and thus the treatment is limited. Thereby, it has been considered that the agonist of the PPAR-a is a local and efficient treatment method, compared to the glucocorticoid (Sigma, USA).
In addition, the skin aging is classified into a photo-aging observed in the skin that is exposed to the ultraviolet for a long time and an intrinsic aging (chronological aging) observed in the skin that is not exposed to the ultraviolet. In the photo-aging and intrinsic aging, the skin becomes thin clinically and there occurs a wrinkle in the skin due to a decreased elasticity of the skin. It is thought that deficiency of the matrix protein, which is produced from the cell in the dermis, is a main cause of the wrinkle. Of the matrix protein in the skin, the collagen occupies 90% or more and the elastin occupies about 3˜4%. In general, the wrinkles are closely related with the collagen reduction in the skin tissue and the expression increase of a matrix metalloproteinase (MMP) which is a kind of the protease, which are closely connected with an activity of the fibroblasts in the dermis tissue. Although there are many research results about the collagen reduction and the MMP increase due to the ultraviolet and mechanisms thereof, a correct mechanism thereof has not been known up to now. A mechanism that has been most known is an activation of AP-1 (activator protein) due to the ultraviolet and a competition of TGF-β/smad, which is important for the collagen synthesis, for p300. The AP-1 and smad binding element (SBE) require the p300 so as to act as transcription factors. Since an amount of the p300 existing in the cell is limited, if one transcription factor is activated, the other transcription factor is impeded. Accordingly, the activation of the AP-1 by the ultraviolet causes the expression of the MMP to be increased and thus the synthesis of the collagen is decreased due to the increase of the MMP. Thereby, it is expected that the increase of the collagen amount and the impediment of the MMP expression may suppress the skin aging.